denitrification to occur at such places, external carbon supply would be needed
which is not economically feasible. Coupled partial nitrification and anammox
process have been successfully used for nitrogen removal from mature landfill
leachates as it contains less biodegradable organic matters (Sun et al. 2016; Wen
et al. 2016). This system also helps to promote enrichment of anammox microorganisms by the activity of AOB. Nitrite produced by AOB during partial nitrification
is used up by anammox microbial communities and thus further helps to enhance
anammox bacterial activity (Miao et al. 2020).
Hybrid treatment strategies, where advanced oxidation processes have been
coupled with anammox system, have also been studied to enhance nitrogen removal
efficiency. In a mature landfill leachate site, ozonation and photo-Fenton oxidation
process coupled with anammox system was found to be capable of removing
nitrogen with 87% efficiency (Anfruns et al. 2013). In another study, nano zerovalent iron (nZVI) and ferroferric oxide (Fe 3 O 4 ) have been found to enhance
formation of anammox granulation and facilitate anammox biofilm formation (Gao
et al. 2014). Low dose of nZVI promotes anammox activity by dissolved oxygen
depletion, but nZVI at 75 mg/L concentration has been found to be inhibitory to
anammox activity (Yan et al. 2019). Free Fe
2+
/Fe
3+ released from corrosion of nZVI
regulate intracellular Fenton oxidation reaction. Furthermore, they are important
components of heme-containing enzymes such as cytochrome c proteins, which play
a key role in anammox catabolism.
7.5 Ammonia-Oxidizing Bacteria: The First-Stage
Nitrifying Microorganism
In nature, ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA),
anammox (anaerobic ammonia oxidizer), and comammox (complete ammonia oxidizer) microorganisms are known to oxidize NH 3 . Among these microorganisms,
several strains of AOB have been isolated and cultured as pure cultures, for example,
Nitrosomonas europaea, Nitrosomonas eutropha, Nitrosospira multiformis, etc.
Only recently, a pure culture of comammox has been isolated, namely, Nitrospira
inopinata (Kits et al. 2019). Though several ammonia oxidizers occur in nature, an
understanding of biochemical reactions of ammonia oxidation is known only for
AOB. Out of several known pure culture of AOB, N. europaea is the most widely
studied. They are predominantly chemolithotrophic bacteria, obtaining energy from
inorganic source (NH 3 ) and assimilate carbon from CO 2 . However, growth on
organic carbon has been found in N. europaea in the presence of fructose and
pyruvate (Hommes et al. 2003). AOB are very slow growing, with doubling time
of 7–24 h (Thandar et al. 2016). Morphologically, they bear extensively thick
intracytoplasmic membrane (ICM) which is stacked in layers (Fig. 7.1). These
thick ICM layers harbor the enzyme responsible for ammonia oxidation, i.e.,
7 Nitrogenous Wastes and Its Efficient Treatment in Wastewater
159
which is not economically feasible. Coupled partial nitrification and anammox
process have been successfully used for nitrogen removal from mature landfill
leachates as it contains less biodegradable organic matters (Sun et al. 2016; Wen
et al. 2016). This system also helps to promote enrichment of anammox microorganisms by the activity of AOB. Nitrite produced by AOB during partial nitrification
is used up by anammox microbial communities and thus further helps to enhance
anammox bacterial activity (Miao et al. 2020).
Hybrid treatment strategies, where advanced oxidation processes have been
coupled with anammox system, have also been studied to enhance nitrogen removal
efficiency. In a mature landfill leachate site, ozonation and photo-Fenton oxidation
process coupled with anammox system was found to be capable of removing
nitrogen with 87% efficiency (Anfruns et al. 2013). In another study, nano zerovalent iron (nZVI) and ferroferric oxide (Fe 3 O 4 ) have been found to enhance
formation of anammox granulation and facilitate anammox biofilm formation (Gao
et al. 2014). Low dose of nZVI promotes anammox activity by dissolved oxygen
depletion, but nZVI at 75 mg/L concentration has been found to be inhibitory to
anammox activity (Yan et al. 2019). Free Fe
2+
/Fe
3+ released from corrosion of nZVI
regulate intracellular Fenton oxidation reaction. Furthermore, they are important
components of heme-containing enzymes such as cytochrome c proteins, which play
a key role in anammox catabolism.
7.5 Ammonia-Oxidizing Bacteria: The First-Stage
Nitrifying Microorganism
In nature, ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA),
anammox (anaerobic ammonia oxidizer), and comammox (complete ammonia oxidizer) microorganisms are known to oxidize NH 3 . Among these microorganisms,
several strains of AOB have been isolated and cultured as pure cultures, for example,
Nitrosomonas europaea, Nitrosomonas eutropha, Nitrosospira multiformis, etc.
Only recently, a pure culture of comammox has been isolated, namely, Nitrospira
inopinata (Kits et al. 2019). Though several ammonia oxidizers occur in nature, an
understanding of biochemical reactions of ammonia oxidation is known only for
AOB. Out of several known pure culture of AOB, N. europaea is the most widely
studied. They are predominantly chemolithotrophic bacteria, obtaining energy from
inorganic source (NH 3 ) and assimilate carbon from CO 2 . However, growth on
organic carbon has been found in N. europaea in the presence of fructose and
pyruvate (Hommes et al. 2003). AOB are very slow growing, with doubling time
of 7–24 h (Thandar et al. 2016). Morphologically, they bear extensively thick
intracytoplasmic membrane (ICM) which is stacked in layers (Fig. 7.1). These
thick ICM layers harbor the enzyme responsible for ammonia oxidation, i.e.,
7 Nitrogenous Wastes and Its Efficient Treatment in Wastewater
159